Hip joint socket for artificial hips

ABSTRACT

A HIP JOINT SOCKET FOR ARTIFICIAL HIPS COMPRISES A SUBSTANTIALLY HEMISPHERICAL PLASTIC SHELL IN WHICH A LIKEWISE SUBSTANTIALLY HEMISPHERICAL CAVITY IS PROVIDED. THE CAVITY IS SITUATED ECCENTRICALLY IN RESPECT TO THE SHELL AND ADAPTED TO ACCOMMODATE THE SPHERICAL UPPER END OF AN ARTIFICIAL THIGH. THE FREE EDGE OF THE HIP JOINT SOCKET, OWING TO AN   OBLIQUE CUT MADE IN A PORTION OF THE SHELL, IS SITUATED IN TWO PLANES FORMING AN OBTUSE ANGLE WITH EACH OTHER.

Sept. 28, 1971 w, |NK I 3,608,096

HIP JOINT SOCKET FOR ARTIFICIAL HIPS Filed Jan. 23, 1970 Inventor:

WALDEMAR L INK X57, W 1M United States Patent O 3,608,096 HIP JOINTSOCKET FOR ARTIFICIAL HIPS Waldemar Link, Hamburg, Germany, assignor tWaldemar Link, Hamburg, Germany Filed Jan. 23, 1970, Ser. No. 5,177 Int.Cl. A61f 1/24, /04 US. C]. 3-1 5 Claims ABSTRACT OF THE DISCLOSURE A hipjoint socket for artificial hips comprises a substantially hemisphericalplastic shell in which a likewise substantially hemispherical cavity isprovided. The cavity is situated eccentrically in respect to the shelland adapted to accommodate the spherical upper end of an artificialthigh. The free edge of the hip joint socket, owing to an oblique cutmade in a portion of the shell, is situated in two planes forming anobtuse angle with each other.

BACKGROUND OF THE INVENTION This invention relates to a hip joint socketfor artificial I: hips, consisting of a substantially hemisphericalplastic shell in which a substantially hemispherical cavity, designed toaccommodate the spherical upper end of an artificial thigh, is situatedeccentrically in relation to the substantially hemispherical surface ofthe hip joint socket.

The known hip joint sockets have a hemispherical surface and ahemispherical cavity. They involve the disadvantage of reduced freedomof movement of the leg, by comparison with that available for the thighof a healthy person. This is due to the fact that when the leg is movedforwards the neck of the artificial thigh is able to make impact withthe lower edge of the front side of the hip joint socket cemented intothe pelvic bone. In addition, the wearer of the artificial hip jointsocket frequently suffers pain.

Attempts have been made to remedy this drawback by making the hip jointsocket comparatively small, so that the head with the neck of theartificial thigh can be rotated further forward until it comes to restagainst the edge of the hip joint socket. Such attempts, however, haveproved inadequate, since a reduction in the size of the hip joint socketincreases the danger of dislocation of the thigh or of the upper end ofthe prosthesis, the reduced area of the cap resulting in a higherpressure per unit of area on the pelvic bone.

SUMMARY OF THE INVENTION It is the object of the present invention toprovide a hip joint socket for artificial hips which avoids theabovementioned disadvantage and which affords greater freedom ofmovement without the danger of dislocation and which will not be sosmall that the specific pressure on the pelvic bone will exceed anacceptable level.

To attain this object the present invention provides a hip joint socketof the type referred to in which the free edge of the hip joint socket,owing to an oblique cut in a portion of the shell, is situated in twoplanes forming an obtuse angle with each other.

An obtuse angle of this kind is produced when a lower portion of theedge of a hemispherical shell is subdivided by a cut in a plane ofintersection taking an oblique course in respect of the vertical axis ofthe hemispherical shell. It is true that by the omission of acorresponding sector or edge portion of the hemispherical shell thespherical head of the prosthesis is not embraced on all sides to thesame extent. It has been found, however, that if the shell is cementedinto a position in which its lateral opening is situated in front, i.e.in the direction in which the wearer walks, there is no risk ofdislocation of the aforemen- 3,608,096 Patented Sept. 28, 1971 "icetioned spherical head, as the latter is mainly moved up and down whilethe user is walking, greater freedom of movement being neverthelessafforded to the leg. In addition, soft tissues and particularly nervecenters cannot be pressed in or forced against the edge of the shell, inthe zone of the emitted sector, during the said walking movement, asoccurs, with the resulting pain, in the case of the hip joint socketknown hitherto.

This advantageous effect is obtained in particular when the anglebetween the planes of the free edge of the hemispherical shell is withinthe range of about to140. It is true that in principle a smaller anglecould be adopted. In this case, however, there is a danger ofdislocation. If, on the other hand, the angle is greater then thedrawbacks discussed in the foregoing will not be overcome to asufficient extent.

As experience shows that the hip cap is cemented into the pelvic bone inan inclined position, thtemaximum pressure being transmitted from theprosthesis to the upper side of the hip cap, where the thickness of thewall of the cap is at its maximum, owing to the eccentric position ofthe cavity in relation to the surface, it is of advantage for the edgeof the obliquely cut portion to extend from the zone where the wall isthickest into the thin walled zone on the lower side of the shell.

The outside of the cap, i.e. the side which transmits the major portionof the pressure is preferably given a smooth surface. On the other hand,it is desirable for grooves or blind holes to be worked into the outerwall of the cap, as they result in increased firmness when cement isused for securing the cap.

A further version of the invention therefore provides that about onequarter of the outside of the shell has a smooth surface, this portionbeing situated in the zone of maximum wall thickness.

The provision of blind holes on the outside of the hip joint socket isin itself already known. The known method of providing blind holes,however, has proved unsatisfactory, since when the shell is pressed intothe cavity of the pelvic bone, this cavity being coated with cementwhich is still in a plastic state, air occlusions are left in the blindholes and detract from the adhesive firmness of the cap. The inventionenables air occlusions of this kind to be avoided as a result of thefact that the outermost side of the shell is provided, outside thesmooth portion of the surface, with grooves preferably arranged in themanner of meridians and parallels of latitude, and also with blind holeswhich are intersected by a groove.

BRIEF DESCRIPTION OF THE DRAWING An embodiment of the invention will nowbe described by way of example and with reference to the accompanyingdrawing in which:

FIG. 1 is aside view of a hip joint socket according to the invention,and

FIG. 2 is a plan view thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT The drawing shows a hip jointsocket which consists of a substantially hemispherical shell 1 thehemispherical surface of which is situated eccentrically in respect ofits likewise substantially hemispherical internal cavity 2, so that theportion of the shell 1 to the right in the front part of the drawing hasa greater wall thickness than the portion to the left in the rear partof the drawing.

FIG. 1 shows particularly clearly that the lower free edge of the shell1, owing to an oblique cut made in the left-hand portion of the saidshell 1, is situated in two planes which enclose an obtuse angle ofabout The edge of the obliquely cut portion extends from the front zone,of greater wall thickness, into the rear zone, of reduced Wallthickness.

Of the outside of the shell 1 the sector 3, situated to the right and inthe front, has a smooth surface. This sector 3 is delimited by twogrooves 4 and 5 which, together with further groves 6, take their courseover the shell 1, in the manner of parallels of longitude, or meridians,and intersect two parallels of latitude 7 and 8. The parallels oflatitude 7 and 8 or these annular grooves are concentric in respect of ablind hole 9 situated in the zenith of the shell 1. In addition to thisblind hole 9, further blind holes 10 are provided on the surface, eachof them being intersected by an annular groove 7 or8.

This hip joint socket shown in the drawing is intended for an artificialhip for a left leg. If this artificial hip is inserted in the humanbody, this is done in such a way that the sector 3' comes to rest withits smooth surface facing upwards, owing to the fact that the shell 1 istilted about the axis A-A, which more or less corresponds to thedirection in which the wearer walks, the cut out sector on the outsideof the shell thus assuming the front position according to the saiddirection.

This enables the thigh of the left leg to be rotated further forwardwithout any danger of compression or impaction of soft tissues or nervecenters on the front edge of the hip cap.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive.

What is claimed is:

1. A hip joint socket for artificial hips, comprising a substantiallyhemispherical shell having an internal substantially hemispherical opencavity bounded by a free edge, said cavity being situated eccentricallyin respect of the substantially hemispherical shell and adapted toaccommodate the spherical upper end of an artificial thigh, a portion ofsaid free edge being defined by an oblique cut made in a portion of theshell subdividing said free edge into two parts located in separateplanes forming an obtuse angle with each other.

2. A hip joint socket as claimed in claim 1, wherein the obtuse anglebetween the planes of the free edge of the hip joint socket is withinthe range of about to 3. A hip joint socket as claimed in claim 1,wherein the free edge of the obliquely cut portion of the shell extendsfrom a zone of maximum wall thickness into a zone of reduced wallthickness.

4. A hip joint socket as claimed in claim 3, wherein about a quarter ofthe outside of the shell is provided with a smooth surface, this quarterbeing situated in the Zone of maximum wall thickness.

5. A hip joint socket as claimed in claim 4, wherein the exterior of theshell remote from said smooth surface is provided with grooves arrangedin the manner of meridians, and with parallels of latitude, and alsowith spaced blind holes which are intersected by said grooves.

References Cited UNITED STATES PATENTS 2,668,531 2/1954 Haboush 128-92CA3,528,109 9/1970 Scales 128-92CX FOREIGN PATENTS 124,585 l/1960 U.S.S.R.

OTHER REFERENCES Replacement of Arthritic Hips by the McKee-FarrarProsthesis by G. K. McKee, Journal of Bone and Joint Surgery, Vol. 48B,No. 2, May 1966, pp. 245-259.

RICHARD A. GAUDET, Primary Examiner R. L. FRINKS, Assistant Examiner US.Cl. X.R. 128-92C

